Plant Cuttings

Mouldy concrete is fit for purpose

When mould gets a grip on a building, it can hold it together.

Human ingenuity is quite a remarkable thing and has allowed us to undertake great projects. But we shouldn’t be so impressed with our own handiwork that we can’t look for help from other lifeforms to improve what we’ve created. Take, for example, concrete. Defined as ‘a blend of aggregates, normally natural sand and gravel or crushed rock …bound together by a hydraulic binder e.g. Portland Cement and activated by water to form a dense semi homogenous mass’, concrete is a construction material at the heart of such impressive buildings as the Pantheon in Rome.

Pantheon Dome
Pantheon Dome. Image: Architas / Wikipedia

But, although concrete is very strong, it is prone to cracking, which can weaken the construction – with potentially lethal consequences if we’re talking about such things as concrete radiation-shielding around a nuclear reactor. Although cracked concrete can be replaced, it will probably only crack again, and again. A better fix would be concrete that could fill in its own cracks – ‘heal’ itself, much as the way bones do when fractured. Well, such ‘living-repairing’ concrete is a very real possibility thanks to work by Jing Luo et al..

They prepared concrete in which spores of the fungus Trichoderma reesi were embedded. As cracks formed in the concrete, water and oxygen entered the gaps and promoted germination of the spores. As the fungus grew it precipitated calcium carbonate, which eventually filled the newly-created gap, i.e. it effectively ‘healed the cracks’. This crack-closure caused conditions within the concrete to change such that they no longer supported fungal growth. Instead, the fungus formed spores that remain until a new crack forms and calcium carbonate-precipitating filaments can once more develop and seal the cracks.

Although this discovery has great potential, one does wonder how much fungal material you’d need to add to make a large concrete structure self-healing and whether all that organic material might actually undermine the strength-giving properties of this otherwise inorganic material. But, that’s a consideration and calculation for the engineers; the biologist in me just thinks this is a rather neat fungus-human ‘mutualism’. And, if that fails to take hold, why not just clad the exterior of the concrete with vaterite-generating saxifrages..?*

In any event, repairing the concrete has got to be a much more carbon-sensitive solution than replacing it with more carbon-polluting cement.

*Or, maybe, the outside of the concrete could be sprayed with sea water to mimic the type of concrete used by Roman engineers to construct their famous marine concrete that remarkably continues to strengthen with age?